Mountain Bike to Road tweaking

Pardon me while my Freddiness sticks out for a moment.

I have virtually no budget to get a road bike which means I may be in for another season of road biking with my old Univega mountain bike. In order to improve my speed on flats and descents (and have more fun), is there any reason I can't purchase a used crankset on Ebay that would get me up to a 50 or 53? Or is this just dumb?

Assuming you have something like 44/32/22 it's probably easiest to swap out for 48/36/26. Most mtb fds will accommodate this. You need to ensure that the size difference between the rings is not excessive unless you are going to run single ring. Also check out the BCD most road bike outer/middle rings are 130mm mtbs are 110mm.